class ListNode {
    int val;
    ListNode next;
    ListNode() {}
    ListNode(int val) { this.val = val; }
    ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if (list1==null&&list2==null){
            return null;
        } else  if (list1==null){
           return  list2;
        } else if(list2==null){
            return  list1;
        }

        ListNode head = new ListNode(-1);

        if (list1.val<=list2.val){
            head.next=list1;
        } else {
            head.next=list1;
        }

        ListNode cur=head;
        while(list1!=null&&list2!=null){
            if (list1.val<=list2.val){
                cur.next=list1;
                cur=cur.next;
                list1=list1.next;
            } else {
                cur.next=list2;
                cur=cur.next;
                list2 = list2.next;
            }
        }

        if (list1==null){
            cur.next=list2;
        } else {
            cur.next=list1;
        }

        return head.next;
    }
}

public class Text1 {

}
